The present invention relates to a dental handpiece, and more particularly to a handpiece to be employed for dental treatment or techniques.
Generally, the dental handpiece is used with its associated working tool or instrument such as a grinder, polisher and drilling tool exchanged according to the purpose of use. The dental handpiece includes a casing having an air motor or an electric motor therein, an outer cylinder projecting from a front end of the casing, a rotor shaft of the motor extending in the outer cylinder, and a main shaft of the working tool detachably inserted into a front portion of the rotor shaft.
From a safety point of view in the handpiece, the working tool must be reliably assembled with the rotor shaft, and it must be also easily assembled and disassembled manually.
Referring to FIG. 7 showing a conventional dental handpiece, a rotor shaft 3 is formed at its front end portion with a cylindrical portion 18 for inserting a main shaft b of a working tool therein. The cylindrical portion 18 is formed at its front end portion with slits 25 to form holding portions 26. A nut 27 is threadedly engaged with an outer circumference of the cylindrical portion 18. When the nut 27 is firmly tightened, the holding portions 26 are pressed radially inwardly by an inner peripheral surface 28 formed at the front end of the nut 27. As a result, an inner surface of the holding portions 26 is brought into abutment against the main shaft b, thus fixing the main shaft.
In the conventional handpiece as mentioned above, as the rotor shaft 3 is idly rotated, it is necessary to insert a pin 29 so as to lock the idling of the rotor shaft 3 upon tightening the nut 27. Further, as the main shaft b of the working tool is very small in diameter, the diameters of the rotor shaft 3 and the nut 27 are also small. Accordingly, a sufficient holding force cannot be obtained by manually rotating the nut 27, and it is therefore necessary to use a spanner (not shown) for firmly tightening the nut 27. Thus, it is hard to easily exchange the working tool during the operation.